Inclusive decays and lifetimes of doubly-charmed baryons

The analysis of singly-charmed hadrons has been extended to the case of doubly-charmed baryons, , and . Doubly-charmed baryons are described as a system containing a heavy cc diquark and a light quark, as in the case of a heavy–light meson. This leads to preasymptotic effects in semileptonic and nonleptonic decays that are essentially proportional to the meson wave function. Interplay between preasymptotic effects in semileptonic and/or nonleptonic decay rates leads to very clear predictions for semileptonic branching ratios and lifetimes of doubly-charmed baryons. Received: 21 January 1999 / Published online: 20 May 1999     

Baryon properties in the relativistic quark model

Properties of heavy and strange baryons are investigated in the framework of the relativistic quark-diquark picture. It is based on the relativistic quark model of hadrons, which was previously successfully applied for the calculation of meson properties. It is assumed that two quarks in a baryon form a diquark and baryon is considered as the bound quark-diquark system. The relativistic effects and diquark internal structure are consistently taken into account. Calculations are performed up to rather high orbital and radial excitations of heavy and strange baryons. On this basis the Regge trajectories are constructed. The rates of semileptonic decays of heavy baryons are calculated. The obtained results agree well with available experimental data.     

Study of Doubly Heavy Baryon Spectrum via QCD Sum Rules

In this work,we calculate the mass spectrum of doubly heavy baryons with the diquark model in terms of the QCD sum rules.The interpolating currents are composed of a heavy diquark field and a light quark field.Contributions of the operators up to dimension six are taken into account in the operator product expansion.Within a reasonable error tolerance,our numerical results are compatible with other theoretical predictions.This indicates that the diquark picture reflects the reality and is applicable to the study of doubly heavy baryons.     

Strange baryon production in hadronic Z0 decays

The production of the $J^{P}={1?er 2}^{+}$ octet baryons Λ and Ξ^?, the $J^{P}={3?er 2}^{+}$ decuplet baryons Σ(1385)^±Ξ(1530)⁰, and Ω^?, and the $J^{P}={3?er 2}^{-}$ orbitally excited state Λ(1520) has been measured in a sample of approximately 3.65 million hadronic Z⁰ decays. The integrated rates and the differential cross-sections as a function of x _E, the scaled energy, are determined. The differential cross-sections of the Λ and Ξ^? baryons are found to be softer than those predicted by both the JETSET and HERWIG Monte Carlo generators. The measured baryon yields are found to disagree with the simple diquark picture where only one tuning parameter for spin 1 diquarks is allowed. The yields are further compared with a thermodynamic model of hadron production which includes the production of orbitally excited mesons and baryons. The momentum spectra of Λ, Ξ^?, Σ(1385)^±Ξ(1530)⁰, and Λ(1520) are also compared to the predictions of an analytical QCD formula.     

Charmless decays B \to{\mathrm{PP}}, {\mathrm{PV}}, and the effects of new strong and electroweak penguins in topcolor-assisted technicolor model

Based on the low energy effective Hamiltonian with generalized factorization, we calculate the new physics contributions to the branching ratios and CP-violating asymmetries of the two-body charmless hadronic decays from the new strong and electroweak penguin diagrams in the topcolor-assisted technicolor (TC2) model. The top-pion penguins dominate the new physics corrections, and both new gluonic and electroweak penguins contribute effectively to most decay modes. For tree-dominated decay modes , etc. the new physics corrections are less than 10%. For decays , etc. the new physics enhancements can be rather large (from to ) and are insensitive to the variations of and within reasonable ranges. For the decays and is strongly dependent: varying from to in the range of –. The new physics corrections to the CP-violating asymmetries vary greatly for different B decay channels. For five measured CP asymmetries of the decays, is only about 20% and will be masked by large theoretical uncertainties. The new physics enhancements to interesting decays are significant in size (), insensitive to the variations of the input parameters and hence lead to a plausible interpretation for the unexpectedly large decay rates. The TC2 model predictions for branching ratios and CP-violating asymmteries of all fifty-seven decay modes are consistent with the available data within one or two standard deviations. Received: 18 August 2000 / Revised version: 22 October 2000 / Published online: 5 February 2001     

Fragmentation Production of Θ0c(uuddc-) and Θ+b(uuddb-) Pentaquarks in the Diquark Model

Heavy hadrons have been the focus of attention because of their worthwhile properties. So far the fragmentation function (FF) and total fragmentation probability (F.P) for heavy baryons and mesons have been calculated in quark model and diquark model in leading order of perturbative QCD. After the discovery of pentaquarks, their fragmentation probabilities were estimated based on the known measurementsof c or b quarks into mesons and baryons. In this note we calculate the direct fragmentation function of \( \overline{c}\to {\varTheta}_c^0\left( uudd\overline{c}\right) \) and \( \overline{b}\to {\varTheta}_b^{+}\left( uudd\overline{b}\right) \) processes in leading order of perturbative QCD, employing the diquark model with considerable precision. Consistent with such a process we set up the kinematics of the fragmentation of a heavy antiquark into a pentaquark such that the effect of the Fermi motion of the constituents is ignored. We show that using the diquark model for studying pentaquark can provide reasonably good theoretical results. The findings of this study accord with those in the previous studies.

     

Radiative decays of heavy baryons with heavy quark symmetry

The decay widths for the radiative decays of heavy baryons are calculated in the heavy quark effective theory. Introducing the interpolating fields for heavy baryons we obtain the transition matrix elements and the corresponding decay widths. Considering theSU(6) flavor-spin wave functions for heavy baryons, the coupling constants are calculated in the nonrelativistic quark model. Since the masses of the heavy baryons are not available, we have taken the predicted bag model masses. We find our results are quite different from that of the heavy quark bag model calculations.     

Electroweak penguin effects in charmless B ±,0→PP and PV decays

Using the next-to-leading order low energy effective Hamiltonian for |ΔB|=1, ΔC=ΔU=0 transitions, the contributions of electroweak penguin operators in charmless B ^±,0→PP and PV decays are estimated in the standard model. We find that, for some channels, the electroweak penguin effects can enhance or reduce the QCD penguin and/or tree level contributions by at least 30%, and can even play a dominant role.     

Baryon formation and dissociation in dense hadronic and quark matter

We study the formation of baryons as composed of quarks and diquarks in hot and dense hadronic matter in a Nambu-Jona-Lasinio (NJL)-type model. We first solve the Dyson-Schwinger equation for the diquark propagator and then use this to solve the Dyson-Schwinger equation for the baryon propagator. We find that stable baryon resonances exist only in the phase of broken chiral symmetry. In the chirally symmetric phase, we do not find a pole in the baryon propagator. In the color-superconducting phase, there is a pole, but it has a large decay width. The diquark does not need to be stable in order to form a stable baryon, a feature typical for so-called Borromean states. Varying the strength of the diquark coupling constant, we also find similarities to the properties of an Efimov state.     

Charmed Baryon in Diquark Model

A diquark model is used to investigate single-charmed baryons.In this model,baryon is composed of two diquarks and an antiquark.Masses of lowest lying states with J~P=1/2~(±) are obtained.Baryons in our results are as heavy as other theoretic predictions and we suggest that the five-quark components should be considered in any three-quark model for studying the charmed baryons.     

Diquark structure in heavy quark baryons in a geometric model

Using a geometric model to study the structure of hadrons, baryons having one, two and three heavy quarks have been studied here. The study reveals diquark structure in baryons with one and two heavy quarks but not with three heavy identical quarks.     

Discussions on the stability of diquarks

Since the birth of the quark model, the diquark, which is composed of two quarks, has been considered as a substantial structure of a color anti-triplet. This is not only a mathematical simplification for dealing with baryons, but also provides a physical picture where the diquark would behave as a whole object. It is natural to ask whether such a structure is sufficiently stable against external disturbance. The mass spectra of the ground states of the scalar and axial-vector diquarks, which are composed of two-light (L-L), one-light-one-heavy (H-L) and two-heavy (H-H) quarks, respectively, have been calculated in terms of the QCD sum rules. We suggest a criterion as the quantitative standard for the stability of the diquark. It is the gap between the masses of the diquark and √s₀ where s₀ is the threshold of the excited states and continuity, namely the larger the gap is, the more stable the diquark would be. In this work, we calculate the masses of the H-H type to complete the series of the spectra of the ground state diquarks. However, as the criterion being taken, we find that all the gaps for the various diquarks are within a small range. In particular, the gap for the diquark with two heavy quarks, which is believed to be a stable structure, is slightly smaller than that of the other two types of diquarks. Therefore we conclude that because of the large theoretical uncertainty, we cannot use the numerical results obtained with the QCD sum rules to assess the stability of diquarks, but need to invoke other theoretical framework.     

Study of heavy-light hadrons within a flux tube model

A classic mass loaded flux tube model and the diquark picture are employed to explore both mesons and baryons. The spectrum of A<'+><,c> baryons and D<,s> mesons is systematically obtained. The spin-orbit interaction in Ds was simplified as and (L→·S→) coupling.The spin-orbit interaction in Ac was simplified as a (J1→·Jc→) coupling. The predicted masses are consistent with the latest experiments.     

Quark matter in QC<Subscript>2</Subscript>D

Results are presented from a numerical study of lattice QCD with gauge group SU(2) and two flavors of Wilson fermion at non-zero quark chemical potential μ ≫ T. Studies of the equation of state, the superfluid condensate, and the Polyakov line all suggest that in addition to the low-density phase of Bose-condensed diquark baryons, there is a deconfined phase at higher quark density in which quarks form a degenerate system, whose Fermi surface is only mildly disrupted by Cooper pair condensation.     

Extraction of α From the CP Asymmetry in B0/B0→π+π- Decays

The influence of strong and electroweak penguin amplitudes in B/B→π⁺π^- is investigated in connection with the determination of the unitarity triangle angle a of the CKM matrix. A relation between the observable asymmetry, the angle α, and the penguin amplitude is established. A model calculation of the penguin amplitude shows that the CP asymmetry in B⁰→π⁺π^- decays is only mildly influenced by the penguin amplitudes. Experimental limits on pure penguin and penguin dominated processes are consistent with the model. This information also suggests in a rather model-independent way that penguin amplitudes will not be a serious complicating factor in the determination ofa from the π⁺π^- time-dependent asymmetry.     

Contribution of Penguins to the Nonspectator Effects in B-, BO, Λb Decays and the Missing Charm Problem

Taking the nonspectator contributions from the "tree" level four-quark operators and the penguin-induced operators into account we recalculate the charm number n_c in B decays. We find that for B^- and Λ_b, penguin contribution can be neglected, while for B_d^o it is dominant if the nonfactorization factor (t^at^a)is not sizably large. Some new physics may be needed to meet the present data.     

On the penguin phases and missing CP asymmetries in exclusive hadronic B decays

Within the standard model, we elucidate the picture of exclusive hadronic B-meson decays, which occur through both the tree and penguin channels. We emphasize that the weak penguin phase is entangled with the strong one and they can be parted only in special approximation. Ignoring this point will lead to significant missing of direct CP violation in either charged-B or neutral-B decays. The effects of these phases on CP-violating partial rate asymmetries are examined, and the relevant ambiguities in the previous literature are clarified.     

Weak decays of charmed baryons

We use the quark model framework to calculate the weak decays of the lowest lying charmed baryons into ground state baryons and mesons. We present detailed results on the predicted flavour and multipole composition of the final state configurations which can be tested in the near future. For the decays 1/2⁺→1/2⁺+0^? we also give symmetry and current algebra estimates which we compare with the quark model results. Semileptonic branching ratios in charmed baryon decays are calculated to be of the order of ～5%. The total lifetime of charmed baryons is predicted to be ～7 10^?14 s which is 5–10 times smaller than the free quark model estimate.